Internal strengthening of insulating board with cereal flour



United States Patent 3,197,366 INTERIQAL STRENGTHENHIJG OF INSULATENG BQARD WITH CEREAL FLOUR Christian F. Girard and Alexander Rose, Ottawa, Ontario, Canada, assignors to Canadian International Paper Company, Montreal, Canada, a corporation of Canada No Drawing. Fiied Apr. 2, 1963, Ser. No. 269,885

6 Claims. (Cl. 162-475) This application is a continuation-in-part of co-pending application, Serial No. 41,249, filed July 7, 1960 and now abandoned.

This invention relates to a process for increasing the structural strength of insulating board.

The expression insulating board used herein is used in consonance with the definition thereof set forth at page 209, The Dictionary of Paper (2nd Ed); American Paper and Pulp Association; New York, 1951. This definition runs as follows: A type of board composed of some fibrous material, such as wood or other vegetable fiber, sized throughout, and felted or pressed together in such a way as to contain a large quantity of entrapped or dead air. It is made either by cementing together several thin layers or forming a nonlaminated layer of the required thickness. It is used in plain or decorative finishes for interior walls and ceilings in thicknesses of 0.5 and 1 inch (in some cases up to 3 inches) and also as a water-repellent finish for house sheathing. Desirable properties are: low thermal conductivity, moisture resistance, fire resistance, permanency, vermin and insect resistance, and structural strength. No single material combines all these properties but all should be permanent and should be treated to resist moisture absorption. (This material is sold under a wide variety of trade names; a list of such names will be found in the pamphlet, Wall Boards and Insulating Materials, issued by the United States Department of Commerce) It is old in the art of manufacturing insulating board, an art which goes back to about 1909 in Canada, to add raw or cooked starches, as well as other binding agents. Commercially prepared starches have been used in the insulating board industry in one form or the other to increase the internal or transverse strength of the product. But it has now been found that, under specific conditions, the addition of low-grade cereal flour produces surprising and wholly unexpected results.

Raw starch is relatively ineifective as an internal strengthening agent for insulating board and the universal practice has been to cook it with or in Water; this swells and breaks up the starch granules, exposing the active bonding material inside. Sometimes a hydrolyzing agent such as sodium hydroxide or an oxidizing agent like sodium hypochlorite is used to assistthe breakdown of the starch. The cooking must be carefully controlled in order to obtain starch particles of a size commensurate with the fiber dimension in question; a fine dense mat composed of soft, Well-purified, closely-packed fibers will require a bonding agent of small particle size, whereas, in a porous mat composed of coarse, loosely-packed fibers, such small particles would be nearly useless, since very little starch would be retained on the fibers and even that would constitute too little size to bridge the gaps between fibers. Again, purified starches are often used in insulating board manufacture. Such starches are those from which proteins, bran fractions, etc., have been substantially removed and these factors have been removed because they have been found to detract from the beneficial eifects of the starch.

Aside from its action of enhancing insulating board internal strength, starch in such environment is known to increase stiffness. For this purpose, it is cooked somewhat more than it would be to achieve insulating board internal strength alone. Where both characteristics are desired, compromise cooking conditions are utilized, but, in any case, the cooked starch is generally added to the insulating board stock at some point in the process after any stock beating or jordaning operations, so as to avoid as much as possible the further breakdown of the starch particles by mechanical action.

In accordance with the present invention, it has been found that relatively expensive starches such as the purified starches can be replaced in the manufacture of insulating board by a much cheaper material such as lowgrade cereal flour without impairment of characteristics desired in insulating board and, indeed, with a resulting distinct improvement in such characteristics. Retention of starch, calculated as starch on insulating board furnish (dry basis) is greatly increased. And strength is substantially increased, so that a desired breaking load or modulus of rupture figure can be obtained in a lighter, more economical board weight.

Further, in a preferred embodiment of our invention, the cereal flour is cooked with a rosin soap, the cooked mixture is added to the pulp, and then papermakers alum (aluminum sulphate) is added thereto. The resulting stock suspension then proceeds through the customary operations of making insulating board.

In the process of our invention, wheat flour is preferred on account of cost as well as quality. Quality for this purpose bears no relation to food use. In fact, animal-feed flours composed of low-grade cuts and bran fractions give results equal to or better than those obtained with highly refined flour. Flour used in accordance with our process is applied in approximately the same proportions as the starch hitherto used, commonly in the range of about 1 to 5% on pulp, dry weight. Rosin soaps suitable for use are commercial grades of a low degree of refinement. One found particularly satisfactory is known as 70% Dark Rosin Size 704 manufactured by Hercules Powder Company Ltd. As in the case of the flour, the lower grades of rosin soap have given distinctly better results than the higher, lighter grat es. About 10% rosin on weight of flour is required for maximum improvement of internal strength. That added above 10% merely adds to sizing effect which is more efficiently achieved by other means, e.g., wax. Alum is added in sufiicient quantity to give a pH of the stock suspension of about 4.2 to 4.8.

No explanation is readily apparent for the outstanding efficacy of rosin soap in this connection. The answer may lie in the combination of the hydrolyzing activity of the alkali with the colloid-stabilizing action of the abietic acid part of the rosin soap molecule. However, the fact that the best results have been obtained with the lower-grade rosin soaps indicates that the impurities also play a part. Furthermore, it must be kept clearly in mind that cooking with rosin soap is beneficial only when applied to flour and may be detrimental in the case of purified starch.

What was said above about the necessity of regulating the cooking of starch in water to get optimum particle size applies with equal force to the cooking of flour with rosin soap solution. A temperature of from about to 210 F. is maintained for about 1 to 20 minutes, after which the action may be quenched by diluting with cold water to bring the temperature to 130 F. or below. A temperature of F. maintained for 10 minutes, followed by quenching has proven satisfactory in most cases, as judged by improvement in board strength.

Further details of our process and the improvements obtained by its use are given in the examples summarized in Table I. 'In all cases the starch or flour used was 2% on pulp, dry weight. The wheat flour used in this work was an animal feed-grade flour known as Warrior Patented July 27, 1965 flour, supplied by the Ogilvie Flour Mills Co. of Mentreal, Canada; it is a mixture of low grade cuts, shorts duster, bran duster, etc. A smooth slurry was first made of the starch or flour with a small part of the water and diluted with more water to a thin suspension before application of heat. In the case of certain types of flour, we found that a small amount of the rosin soap helps materially in promoting a smooth, lump-free slurry. Cooking with water was carried out in accordance with customary industrial usage, holding at a temperature of about 160 to 210 F. (but not boiling) for 15 minutes, or less, depending on pulp quality and production requirements. Cooking with rosin soap was carried out as described above, at 190 F. maintained for 10 minutes, followed by quenching to below 130 F., using 10% rosin soap on flour. This, again, can be varied to suit pulp quality. The resulting suspension was added to pulp stock, and alum added as hereinbefore described, just before formation of the insulating board on the machine. The finished insulating board was tested for transverse breaking load from which modulus of rupture (M.O.R.) was calculated. Each test was run in direct comparison with a control (insulating board containing no starch or other additive). Since tests'on control and experimental boards vary with humidity and other test conditions, only percentage increase over plain board control is given, each figure representing an average of many tests. Results are given in tabular form for convenient comparison.

Table I Percent Preparation before Percent d Example Additive Used addition to pulp M.O.R. i ,I Increase Analysis l Wheat flour Cooked with water 14. 1

plus 0.1% Sod. sul phite on flour. 2 Wheat starch Coollred with water 14. 6

on y. 3 do Cooked with 10% 10. 8

rosin (on starch). 4 Corn starch... Cooked with 10% 28. 7

resin. 5 do Cooked with water 39.1 40

only. G Wheat flour... Cooked with 33. 6

high grade resin 1 (on flour). 7 do Cooked with 10% low 42. 0 95 grade rosin 2 (on ilonr).

Pexol dry rosin size, a fortified paste size made from highly refined and chemically modified pale resins and having the following properties: an acid number (D.B.) of from 18 to a total solids content of 70%, 77%, or 80% l%; and a percentage of free alkali (as biscarbonate) of 0 to 1.0- Hercules Powder Co.

70% dark rosin size 704, an unfortified paste size made from dark resins and having the following properties an acid number (13.13.) of 0 to 21 or 14 to a total solids content of 70% or 80% i1% and, a percetange of free alkali (as bicarbonate) of 0 to 2.5l-Iercules Powder Co.

The results included in Table I show that Wheat flour is greatly improved as an internal strengthening agent by cooking with rosin soap, giving results equal to or surpassing the best obtainable with the commonly used additive corn starch. As can be seen in Table No. 1, the best gain in transverse strength was by the use of cooked cereal flour and rosin, and at much less cost than the next best with cooked corn starch.

We have found that although the batch type of cooking the flour-rosin mixture is ideal, the so-called Cascading method of cooking might be satisfactory for more autoniation. This type consists of three propeller agitated tanks in series. The cereal flour-rosin mixture would be mixed and dispersed in the cold in the first tank, followed by cooking in the second tank, and finally dilution and quenching in the third tank. This system can be fully automated with a proper system of controls. A saving in manpower could probably be obtained with this automated method.

In a preferred utilization of the present invention, and one in conformity with Table I, the process begins with making the insulating board furnish, as by combining various types of wood pulp. The proportions required, of course, depend upon the product being manufactured at the time. But for example, an insulating board furnish can include 45% conventional groundwood pulp (pulp resulting from the hydraulic pressing of whole logs against rapidly rotating grindstones and comprising fibers sheared or rubbed oil? the logs by the grindstones); about 25% attrition mills pulp (pulp resulting from wood chips charged into digesters heated with live steam under pressure, blown into a cyclone, and fed through attrition mills or refiners); and, about 30% newsprint mill pulp (pulp coming from newsprint manufacture screening operation reiects). Such a furnish has the desirable characteristics of (1) a high drainage rate, so as to permit its rapid formation into a thick sheet on an Oliver mat forming machine; (2) a proper distribution of long and short wood cellulose fibers, so as to provide an insulating board neither including too many long fibers and being soft and flexible like a blanket nor including too many short fibers and being brittle and weak; and, (3) a maximum of inherent adhesiveness, so that the insulating board product will he structurally strong and will not crumble at the edges and corners. Previous to the combination step, each pulp is diluted with large quantities of water; screened to remove coarse fibers, so that they may be recycled for further refining; thickened to a consistency of about 3% by draining; and, stored in tanks awaiting the combination.

Once the pulps are combined to provide an insulating board furnish, any one or more of a number of additives can be flowed into such furnish. These additives can inciude Wax and paperrnakers alum to give the product water resistance or asphalt to give it weather resistance. They can also include the low-grade cereal flour of the present invention which gives the product flexural strength.

Next, the additive containing furnish or stock is diluted with water to about 1% consistency and flowed into an Oliver vat from which a rotating drum covered with bronze wire mesh picks up the stock in the form of a sheet or mat of uniform thickness. The surface of the drum under the wire mesh is lined with suction boxes under a vacuum which draws the fibers from the stock and firmly against the wire and draws away excess water.

With the formation of the sheet, the remainder of the process is primarily a matter of water removal. Perhaps with the aid of a doctoring device, the wet mat is taken oil the drum, passed between endless wire screen, and travelled through pressure roll nips which squeeze water out of the mat until it is about 40% dry. Thereafter, it is cut into suitable lengths which are passed to driers or kilns held at about 300 F. at the wet end and 320 F. at the dry end. it takes about 2 /2 hours in such a kiln to dry a /2" insulating board, i.e., so that it has about 2% to 3% moisture content. The lengths of insulating board are then processed, so as to give them decorative or acoustical properties, and cut into desirable tile sizes.

What is claimed is:

1. A process of internally strengthening insulating board containing pulp fiber consisting essentially of cooking a cereal flour without boiling to obtain cereal flour particles commensurate in dimension with the pulp fiber dimension, quenching the cooked cereal flour by diluting it with cold water and bringing its temperature down to at least F, adding the quenched cooked cereal fiour to an aqueous insulating board pulp furnished slurry, and making the insulating board from the slurry, the cereal flour being added in an amount of from about 1% to 5% by weight of the pulp on a dry basis.

2. The process of claim 1 in which the cereal flour is mixed with a rosin soap and the rosin soap content of the mixture is not more than about by weight of the cereal flour.

3. The process of claim 1 in which the cereal flour is wheat flour.

4. A process of internally strengthening insulating board consisting essentially of mixing Wheat flour with a rosin soap, cooking the mixture at a temperature of from about 169 F. to 210 F. for from about 1 to 20 minutes, quenching the cooked mixture by diluting it with cold water and bringing its temperature down to at least 130 F., adding the quenched cooked mixture to an aqueous insulating board pulp furnish slurry, and making insulating board from the slurry, the wheat flour being in an amount of from about 1% to 5% by weight of the pulp on a dry basis and the rosin soap content of the mixture being not more than about 10% by weight of the cereal flour.

5. Insulating board comprising pulp furnish and cereal flour, having internal strength, and made by process consisting essentially of cooking a cereal flour without boiling, to obtain cereal flour particles commensurate in dimension with the pulp fiber dimension, quenching the cooked cereal flour by diluting it with cold water and bringing its temperature down to at least 130 F., adding the quenched cooked cereal flour to an aqueous insulating board pulp furnished slurry and making insulating board from the slurry, the cereal flour being in an amount of from about 1% to 5% by Weight of the pulp on a dry basis.

6. Insulating board comprising pulp furnish, cereal flour, and a rosin soap, having internal strength, and made by a process consisting essentially of mixing a cereal flour with a rosin soap, cooking the mixture without boiling to obtain particles of the combination commensurate in dimension with the pulp fiber dimension, quenching the cooked mixture by diluting it with cold Water and bringing its temperature down to at least F., adding the quenched cooked mixture to an aqueous insulating board pulp furnish slurry, and making insulating board from the slurry, the cereal flour being in an amount of from about 1% to 5% by Weight of the pulp on a dry basis and the rosin being not more than about 10% by weight of the cereal flour.

References Cited by the Examiner UNITED STATES PATENTS 307,607 11/84 Weygang 162174 1,622,496 3/27 Davidson et al 162174 1,672,705 6/28 Bradshaw 162-174 1,887,726 11/32 Weber 16'2145 2,207,555 7/40 Rowland 162175 2,410,357 10/46 Pattilloch 162174 2,980,576 4/61 Etheridge 162-175 FOREIGN PATENTS 51,339 3/36 Denmark. 12,190 1888 Great Britain. 12,299 1891 Great Britain.

OTHER REFERENCES Crustin, Chemical Abstracts, page 7118g, 1947. Casey, Pulp and Paper, vol. 1, 1952, Interscience Publishers, New York, page 491.

DONALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLK, Examiner. 

1. A PROCESS OF INTERNALLY STRENGTHENING INSULATING BOARD CONTAINING PULP FIBER CONSISTING ESSENTIALLY OF COOKING A CEREAL FLOUR WITHOUT BOILING TO OBTAIN CEREAL FLOUR PARTICLES COMMENSURATE IN DIMENSION WITH THE PULP FIBER DIMENSION, QUENCHING THE COOKED CEREAL FLOUR BY DILUTING IT WITH COLD WATER AND BRINGING ITS TEMPERATURE DOWN TO AT LEAST 130*F., ADDING THE QUENCHED COOKED CEREAL FLOUR TO AN AQUEOUS INSULATING BOARD PULP FURNISHED SLURRY, AND MAKING THE INSULATING BOARD FROM THE SLURRY, THE CEREAL FLOUR BEING ADDED IN AN AMOUNT OF FROM ABOUT 1% TO 5% BY WEIGHT OF THE PULP ON A DRY BASIS.
 6. INSULATING BOARD COMPRISING PULP FURNISH, CEREAL FLOUR, AND A ROSIN SOAP, HAVING INTERNAL STRENGTH, AND MADE BY A PROCESS CONSISTING ESSENTIALLY OF MIXING A CEREAL FLOUR WITH A ROSIN SOAP, COOKING THE MIXTURE WITHOUT BOILING TO OBTAIN PARTICLES OF THE COMBINATION COMMENSURATE IN DIMENSION WITH THE PULP FIBER DIMENSION, QUENCHING THE COOKED MIXTURE BY DILUTING IT WITH COLD WATER AND BRINGING ITS TEMPERATURE DOWN TO AT LEAST 130*F., ADDING THE QUENCHED COOKED MIXTURE TO AN AQUEOUS INSULATING BOARD PULP FURNISH SLURRY, AND MAKING INSULATING BOARD FROM THE SLURRY, THE CEREAL FLOUR BEING IN AN AMOUNT OF FROM ABOUT 1% TO 5% BY WEIGHT OF THE PULP ON A DRY BASIS AND THE ROSIN BEING NOT MORE THAN ABOUT 10% BY WEIGHT OF THE CEREAL FLOUR. 